A Holistic Approach to Improving Fracture Resistance in Cold Temperature Applications

One of the greatest challenges of welded steel structures subject to cold temperature operations is the problem of brittle fracture. The reduced fracture toughness of steel materials is well known, whether the material is the weld metal, heat affected zone or base metal. In the quest to achieve greater fracture resistance, a common approach is to increase the material property of toughness. However, fracture resistance also involves two other major factors: stress levels and flaw sizes. For structures in cold temperatures that are also cyclically loaded, fatigue cracks can cause flaw sizes to increase, reducing fracture resistance. A “holistic” approach toward improvement of fracture resistance goes beyond considering material properties alone, but looks at stresses and flaw sizes, and in the case of cyclically loaded structures, also considers stress ranges, connection geometry and the number of load cycles.

The major variables affecting fracture resistance, both of statically loaded and cyclically loaded structures, are considered. The role of material strength, temperature shift, loading rate, connection geometry, structural redundancy and inspection are discussed. Case studies are presented, demonstrating practical ways in which fracture resistance can be improved, even with materials of limited toughness capabilities.